U.S. Pat. No. 4,287,762 describes a digital electronic weather station or weather monitor with digital display and circuitry for selecting and displaying any of a number of monitored weather functions such as indoor and outdoor temperatures, pressure, rainfall, humidity, wind speed and wind direction. The weather parameters are monitored by various transducers coupled to the weather center circuitry. The transducers generally utilize the rotational motion or other displacement of a respective parameter responsive structure and incorporate visible calibration marks for example in a digital code pattern to be read by a stationary optical reader or photo detector which provides electrical output signals for processing. The optical reading techniques used in U.S. Pat. No. 4,287,762 generally transform analog devices typically employing as the moveable analog element a rotatable shaft into digital read out devices and are applicable not only to weather transducers but to condition sensing instruments generally.
The Schroeder U.S. Pat. No. 4,086,580 describes another relative rotational position shaft encoder or incremental encoder which provides a series of discrete output signals as a function of rotation. Attached to the shaft is a disk with solid portions and slots. A light source and a pair of light detectors generate a first signal related to the amount of rotation and a second signal dependent upon the direction of rotation. The determination of rotational position is dependent upon an original reference position or initial zero position and is subject to cumulative error. Another such incremental optical shaft encoder is described in the Stabler U.S. Pat. No. 2,656,106. A magnetic rotational position sensing apparatus is described in the Sullivan U.S. Pat. No. 3,268,887.
The problems associated with incremental or relative rotational position shaft encoders may be overcome by providing absolute rotational position encoders for example as described in the Blake U.S. Pat. No. 3,549,897. Such an absolute electro-optical encoder however requires complex reticle tracks on a rotary disk. A hybrid shaft position encoder is described in the Groff U.S. Pat. No. 4,041,483 but requires multiple engaging disks with coded tracks. A variety of other rotary switches and shaft encoders is described in the prior art.